Subtle interactions between planetary orbits change Earth’s climate and geological processes. Scientists have picked up on such a signal in cyclic periods of heavy erosion on the floor of the deep sea.
The study, published in Nature Communications, found that gaps in sedimentation across the globe have occurred in 2.4-million-year cycles, which the authors say can be explained by the interactions of Mars’s and Earth’s orbits. The findings have implications for scientists’ understanding of Earth’s past and future.
“There’s no other way to explain this cyclicity other than this orbital interaction between Earth and Mars.”
The discovery came from an analysis of publicly available sedimentation data from the past 50 years of ocean drilling at hundreds of sites worldwide.
When analyzed together, data from 293 deep-sea drill holes showed a pattern: About every 2.4 million years, there was a gap in the sediment record, referred to as a hiatus. Researchers had initially identified the gaps as part of a study published in 2022 but only recently discovered their cyclicity after analyzing the patterns in the sediment record.
The hiatuses are likely a result of vigorous deep-sea currents that swept away sediment on a global scale, said geophysicist Dietmar Müller at the University of Sydney, a co-author on the new study. Overall, the researchers observed 27 cycles in the sedimentation data over the past 70 million years.
Because the pattern was cyclic, the team looked to the solar system for clues. Scientists have known for decades that other planets can influence Earth’s orbit and, subsequently, Earth systems, thanks to cycles on the order of 10,000–100,000 years called Milankovitch cycles.
Longer cycles of millions to tens of millions of years, often called astronomical grand cycles, exist too, though less evidence has been found for them in the geological record.
A 2.4-million-year grand cycle involving the orbit of Mars is the most likely explanation for the patterns seen in the sedimentary data, according to the study’s authors. “There’s no other way to explain this cyclicity other than this orbital interaction between Earth and Mars,” Müller said.
Benjamin Mills, a biogeochemist at the University of Leeds who was not involved in the research, said the data add to the limited records that show astronomical grand cycles affecting Earth.
Mills was part of a team that observed similar 2.4-million-year cycles in ocean oxygen levels and biodiversity. He’s working on new research that links these cycles of biodiversity to orbital changes. There are “lots of interesting extensions” of the work by Müller and his colleagues, Mills said.
The researchers’ methods were original, as most work to reveal orbital forcing on Earth’s paleoclimate is done by looking at sediment itself, rather than gaps in sediment, said Margriet Lantink, a geologist at the University of Wisconsin–Madison who was not involved in the new research. The data the team used to show the cyclicity are “relatively convincing,” she said.
A Hot Hypothesis
The specific interaction the researchers point to involves Earth’s perihelion—the point in Earth’s orbit where it’s closest to the Sun. Every 2.4 million years, Mars’s orbit pulls Earth’s perihelion slightly closer to the Sun, increasing the solar radiation that hits Earth.
That extra solar radiation isn’t much, but the researchers hypothesized that it’s enough to kick-start feedback loops on Earth that alter Earth’s processes—such as ocean currents. Warming spurred by the orbital changes could have led to an increase in cyclone activity that caused more vigorous ocean currents and seafloor erosion, Müller said.
“The important thing for the rest of us in the field to do now is to start testing some of these ideas.”
Scientists will need to do more work to demonstrate the link between orbitally forced warming and deep-sea currents, Mills said. The study’s authors “have done a good job in suggesting what might cause the actual hiatuses, but so far it’s just a suggestion,” he said. “The actual process of how you get from orbital change to what they see in the sedimentological record—there could be many steps to that.”
“The important thing for the rest of us in the field to do now is to start testing some of these ideas,” Mills said.
As well as offering an understanding of Earth’s past, the findings could help predictions of Earth’s future and, particularly, how Earth systems will respond to warming, Müller said. Humans are contributing to climate change much faster than any geological or astronomical processes, Müller said. But data on Earth’s past can still inform simulations of future climate effects by allowing scientists to rule out other drivers, such as Milankovitch cycles or astronomical grand cycles, he said.
“Ultimately, it helps us differentiate anthropogenic changes to the system from naturally occurring changes,” he said.
—Grace van Deelen (@GVD__), Staff Writer